1. Field of the Invention
The present invention relates to improvements in a bolting structure having a non-magnesium alloy and conventional member disposed on a magnesium alloy member, the magnesium alloy member being covered with an insulator, and a bolt initially inserted through the magnesium alloy member and then into the conventional member, thereby permitting the conventional member and the magnesium alloy member to be bolted together.
2. Description of the Related Art
A magnesium alloy member is preferably used for, e.g., a reduction in weight of a vehicle because of the lightest-weight metal in practical use. A bolting structure is useful in assembling the magnesium alloy member onto a conventional member such as a steel material. However, the bolting structure suffers from problems as given below.
FIG. 12 is a cross-sectional view, illustrating a conventional bolting structure. The typical bolting structure is shown having a non-magnesium alloy and conventional member 102 disposed on a magnesium alloy member 101, and further having a bolt 103 initially inserted through the magnesium alloy member 101 and then into the conventional member 102, thereby fastening these two members 101, 102 together. The bolt 103 is a low cost hexagonal bolt made of carbon steel.
In some cases, coagulation of dew in the air between a head 104 of the bolt 103 and the magnesium alloy member 101 causes water 105 to be lodged therebetween. The magnesium alloy member 101 is the most base material in potential, and a galvanic cell is formed between the magnesium alloy member 101 and the dissimilar metal or bolt 103. As a result, an electrical current is run between the magnesium alloy member 101 and the dissimilar metal or bolt 103 through the galvanic cell, and corrosion called stray current corrosion occurs therebetween. In order to avoid such a phenomenon, the magnesium alloy member 101 must be covered with an electrically insulating material for electrically isolating the member 101 from the dissimilar metal.
FIGS. 13A and 13B illustrate conventional bolting structures having problems to be overcome.
As shown in FIG. 13A, the magnesium alloy member 101 is covered with an insulator 106 such as by plating. When the bolt 103 is inserted into the member 101, then threads (thread ridges) of the bolt 103 at a distal or lower end thereof sometimes damage the insulator 106. Such damage is often accompanied by the insertion of the bolt 103.
Once the insulator 106 is damaged, the insulator 106 at such a damaged portion thereof is deficient in insulating performance. Then, the stray current corrosion undesirably occurs thereat.
In FIG. 13B, when the bolt 103 is brought into threaded engagement with the magnesium alloy member 101 through a washer 107, then the washer 107 is rotated in union with the revolving bolt 103. The rotated washer 107 may damage the insulator 106, thereby promoting the stray current corrosion at such a damaged location.
Thus, the stray current corrosion is likely to occur, even at the magnesium alloy member 101 having the insulator 106 disposed thereon.
In view of the above, an object of the present invention is to provide a stray current corrosion-free or stray current corrosion-resistant bolting structure for a magnesium alloy member covered with an insulator.
In order to achieve the above object, the invention provides a bolting structure for a magnesium alloy member, having a non-magnesium alloy and conventional member disposed on the magnesium alloy member, the magnesium alloy member being covered with an insulator, and a bolt initially inserted through the magnesium alloy member and then into the conventional member, thereby permitting the conventional member and the magnesium alloy member to be bolted together, comprising: a washer disposed between a head of the bolt and the magnesium alloy member; and, a lateral washer displacement-proof member for preventing the washer from being laterally displaced, the lateral washer displacement-proof member being positioned either on one of the washer and the magnesium alloy member or between the washer and the magnesium alloy member, wherein the magnesium alloy member is formed with a through-hole that is greater in diameter than a bolthole of the washer.
The lateral washer displacement-proof member prevents lateral displacement of the washer mounted on the magnesium alloy member, and thereby holds the washer in desirable position. The bolt is inserted into the magnesium alloy member by being guided by the bolthole of the washer. The bolt at a distal end thereof is not likely to contact the through-hole of the magnesium alloy member because the through-hole is sufficiently greater than the bolthole. As a result, the insulator remains intact because of non-contact of the bolt with the through-hole, and no stray current corrosion occurs.
In addition, the invention provides a bolting structure for a magnesium alloy member, wherein the through-hole is any non-circular hole, including a polygonal hole, designed to lock the washer against rotation.
Since the washer rotated jointly with the bolt scratches the insulator, a member is provided for locking the washer against rotation in order to prevent the occurrence of scratches and stray current corrosion.
Further, the invention provides a bolting structure for a magnesium alloy member, wherein the lateral washer displacement-proof member is one of a boss, a cylindrical concave, and at least three protrusions, the boss being formed integrally on the washer, the boss having an outer diameter slightly smaller than a diameter of the throughhole, the cylindrical concave having a diameter slightly greater than an outer diameter of the washer, the cylindrical concave being formed in the magnesium alloy member, and the protrusions projecting outward from the magnesium alloy member in order to prevent sideward displacement of the washer. The terms xe2x80x9cslightly smallerxe2x80x9d and xe2x80x9cslightly greaterxe2x80x9d as previously mentioned take account of a clearance required for conveniently assembling components together.
The boss integrally formed on the washer is engaged with the through-hole, thereby holding the washer in position, which otherwise would be moved sideward. Alternatively, the engagement of the washer with the cylindrical concave holds the washer in position, which otherwise would be displaced sideward. Furthermore, the plurality of protrusions disposed about the washer holds the washer in position, which otherwise would be displaced sideward. That is, these lateral washer displacement-proof members are applied to prevent the washer from being moved sideward or making a gap.
The invention provides a bolting structure for a magnesium alloy member, wherein the washer is affixed to the magnesium alloy member through a double-side adhesive tape.
Such a construction in which the washer is secured to the magnesium alloy member by means of the adhesive tape holds the washer in position, which otherwise would be dislodged from the magnesium alloy member, locks the washer against rotation, and provides enhanced insulating performance of the magnesium alloy member.
Furthermore, the invention provides a bolting structure for a magnesium alloy member, wherein the lateral washer displacement-proof member is a double-side adhesive tape for affixing the washer to the magnesium alloy member.
Such a construction in which the washer secured to the magnesium alloy member by means of the adhesive tape holds the washer in position, which otherwise would result in lateral displacement, rotation, and dislodgement from the magnesium alloy member.